Vapor deposition process



1966 D. A. HAY ETAL 3,290,233

VAPOR DEPOSITION PROCESS Filed Oct. 22, 1965 FLOW OF HEAT DECOMPOSABLE ALUMINUM GAS SHARPLY CONFORMED SUBSTRATE COMPOSED OF IRON, COPPER, ALUMINUM, MAGNESIUM OR ALLOYS THEREOF ALUMINUM DEPOSITED FIG. I 14 SUBSTRATE HEATED IO A8 ALUMINUM ANODIZED I s\\\\\ &\\\w

VIII/I0, ll/114;) ALUMINUM '0 I SUBSTRATE L.

AL O

ALUMINUM COPPER STRIP FIG.4

Anmw i BYWX W MM fi fl zim/n ATTORNEYS United States Patent 3,290,233 VAPOR DEPOSITION PROCESS Donald A. Hay, Wellesley, and Benjamin L. Averbach, Belmont, Mass, assignors, by mesne assignments, to Contemporary Research, Inc., Waltham, Mass., a corporation of Delaware Filed (let. 22, 1963, Ser. No. 317,922 1 Claim. (Cl. 204-38).

The present invention relates to vapor deposition processes and products and, more particularly, to the protection of certain configuration by the provision of aluminum oxide coating. Certain configurations present sharp edges or notches which are difiicult to insulate electrically or to protect chemically in a practical manner by a thin coating. Thus electrically conducting strips for use in inductors often have jagged edges that easily cut through ordinary coatings provided for insulation and threaded nuts and bolts have corrosion sensitive helical notches that are difficult to protect against chemical attack both before and after use.

The primary object of the present invention is to provide processes and products involving the coating of configurations of specified composition with aluminum by vapor deposition and the anodizing of the aluminum to a depth greater than the ordinary depth of aluminum oxide that normally is formed in atmosphere. It has been found that such coating, when of selected thickness and pore free continuity, retains its adherence to its substrate and its ability to protect against abrasive and chemical attack under stringent conditions.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the processes and products involving the steps, components, materials and interrelationships, which are exemplified in the following disclosure, the scope of which will be indicated in the appended claim. For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection wit-h the accompanying drawing, wherein:

FIG. 1 illustrates materials, in exaggerated cross-section, undergoing a process of the present invention;

FIG. 2 illustrates a product embodying the present invention;

FIG. 3 illustrates another product embodying the present invention; and

FIG. 4 illustrates another product embodying the present invention.

Generally, the process of the present invention is illustrated in FIG. 1 as comprising the steps of depositing an aluminum coating 14 from a gas 12 onto a heated substrate and anodizing the coating to a depth 16, which is greater than that of the usual aluminum oxide coating formed in air. The substrate has one form or other of a sharp conformation, illustrated as in notch 18. The heatdecomposable aluminum bearing gas is, for example, an aluminum halide such as aluminum chloride, an aluminum alkyl such as aluminum triethyl or aluminum triisobutyl, an aluminum hydride such as aluminum dimethyl hydride, and an aluminum amine, particularly, an aluminum amine hydride of a type to be described in more detail below. The vapor pressure of the metal bearing gas is established by heating the metal bearing compound to a temperature above which its vapor pressure is appreciable but below that temperature at which decomposition does occur, for example, a temperature ranging from room temperature to 90 C. An auxiliary gas, in the form of a reducing gas such as hydrogen or an inert gas such as nitrogen or argon is provided to sweep the metal bearing gas into contact with the substrate, the total pressure of 3,290,233 Patented Dec. 6, 1966 the system, for example, being less than 120 mm. Hg, preferably less than 50 mm. Hg. Such reducing gas serves to facilitate decomposition of certain aluminum compounds, particularly the aluminum halides. Such an inert gas serves to inhibit decomposition before the metal bearing gas actually reaches the substrate. Generally, for the variety of aluminum compounds listed above, the coating is deposited on the strip, when at temperatures ranging from to 1000 C. However, best results are achieved with materials and conditions such that the temperature of the substrate during deposition ranges from to 180 C. Preferably, the aluminum coating ranges from 10 microinches to 0.005 inch in thickness and best results are achieved when the coating ranges from 30 to 70 microinches in thickness. The anodizing involves directing a current through the aluminum layer, as an anode, in an appropriate electrolytic solution. The resulting aluminum oxide coat 16 preferably ranges from 1 microinch to .5 mil thick. The residual aluminum stratum 14, remaining pore-free, preferably is at least as thick as aluminum coat 16. A variety of anodizing procedures are applicable including anodizing in chromic acid or sulfuric acid solution. Anodizing in tartaric acid solution has been found particularly effective.

Preferred aluminum compounds are aluminum hydride amine complexes, preferably formed from volatile lower secondary and tertiary amines, i.e. amines characterized by less than five carbon atoms. Examples of such useful aluminum hydride amine complexes are trimet-hyl amine aluminum hydride, dimethylamine aluminum hydride, allyldimethylamine aluminum hydride, methyldimethylamine aluminum hydride, triethylamine aluminum hydride, tripropylamine aluminum hydride and diethylamine aluminum hydride.

Generally, the contemplated substrates are composed of iron, iron alloys, copper, copper alloys, aluminum, aluminum alloys, magnesium and magnesium alloys. A typical example of an iron alloy contains, by total weight, in excess of 97% iron for example 98.4%, in excess of 0.1% carbon for example 0.5 in excess of 0.5 silicon for example 0.09%, in excess of 0.005% phosphorus for example 0.1% and in excess of 0.01% sulfur for example 0.07%. Also contemplated are alloy steels, for example, having the foregoing proportions except that the iron is replaced to the extent indicated by less than 20% of chromium or less than 10% of manganese or less than 0.5% of nickel or less than 20% of silicon. Examples of copper alloys are, by total weight: brass containing copper and a remainder of from 18 to 40% zinc; bronze containing 88% copper, 8% tin, 2% zinc and 2% lead; aluminum bronze containing 90% copper and 10% aluminum; silicon bronze containing copper and a remainder of not more than 5% silicon; phosphor bronze containing copper and a remainder of tin and phosphorus. A typical aluminum alloy, by total weight, is duraluminum containing aluminum and a remainder of 4% copper, 0.6% magnesium and 0.6% manganese. A typical magnesium alloy, by total weight, contains magnesium and a remainder of from 4 to 10% aluminum, from 0 to 3% zinc, from 0 to 0.2% manganese, and optionally including traces of silicon, cadmium, tin, lithium, boron and zirconium.

Conducting configurations in the form of a thin strip of metal are advantageous when used in inductors in that they simplify inductor fabrication while maintaining low distributed capacity. Normally, a metal strip of the contemplated type is formed by slitting from copper sheet. In any case, the edges of the strip ordinarily are sharp or burred. These edges tend to cut into or through in-' sulation with which they are in contact. In particular, they tend to preclude simple processes in which insulation is provided merely by application of a lacquer or other coating. FIGS. 2 and 3 illustrate a product embodying the present invention as comprising a pair of ferrite crosspieces 20, 22, between which are disposed a pair of ferrite rods 24, 26. Wound about the ferrite rods are a pair of coils 28, 30 each formed from a strip of the type shown in FIG. 3 as comprising a copper substrate 40, an aluminum stratum 42 and an anodized stratum 44. The inner and outer extremities of the strips are provided with primary and secondary leads shown at 32, 34, 36 and 38.

FIG. 4 illustrates, in exaggerated cross-section, a portion of an externally threaded bolt embodying the present invention. An internally threaded nut embodying the present invention is similar in appearance. This bolt is shown as having helical threads 46 about a shank of generally circular transverse-cross-sectional profile. The shank has a substrate 48 composed of steel, an inner stratum 50 composed of aluminum and an outer stratum 52 composed of aluminum oxide formed by anodiz-ation.

The following non-limiting examples will further illustrate the present invention.

Example 1 As a specific example of the present invention, the strip of FIG. 2 was prepared as follows. The strip, 0.008 inch thick and one-half inch wide, was sliced from a pure copper sheet. The strip, heated to a temperature of 150 C. was subjected to trimethyl amine aluminum hydride vapor at a partial pressure that was established by heating the compound in solid form to a temperature of between 75 and 90 C. Nitrogen was mixed with this vapor to establish a total vapor pressure of approximately 50 mm. Hg. The process was continued until a 50 microinch porefree layer of aluminum was deposited. Thereafter the strip was anodized in a 3% aqueous solution of tartaric acid, the pH of which was adjusted to 5.5 by the addition of ammonia. The temperature of the anodizing solution was 30 C. and the applied voltage was 250 volts A.C. Anodizing was continued until the external layer of aluminum oxide was 25 microinches. oxide coat positively insulated the strip so that it could be wound into the inductors shown in FIG. 3 without additional treatment and with the assurance that even the edges of the concentric convolutions were effectively in sulated from each other.

Example 2 The process of Example 1 was repeated except that the substrate was composed of aluminum.

Example 3 The process of Example 1 was applied to the bolt of FIG. 4 and an analogous nut, which were composed of steel. These products were remarkably free from corrosion even after being mated in such a way that maxi- The resulting aluminum mum abrasion was attempted. Immersion in nitric acid at 150 F. had no visible immediate effect.

Example 4 The process of Example 3 was repeated except that the nut and bolt were composed of magnesium.

The present invention thus provides novel processes and products for protecting desired physical properties of certain structural products in a novel manner.

Since certain changes may be made in the above disclosure without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

A fabricating process involving applying a protective aluminum oxide coating to a metallic substrate characterized by a sharp conformation and composed of a member of the class consisting of iron, copper, aluminum, magnesium and alloys thereof, said process comprising the steps of subjecting said substrate while at a predetermined temperature to a heat decomposable aluminum containing compound for a predetermined time, said heat decomposable aluminum containing compound being an aluminum hydride amine complex characterized by less than five carbon atoms, said predetermined temperature ranging from to 180 C., said predetermined time being sufiicient to enable the deposition on said substrate of a pore free aluminum coat ranging in thickness from 30 to 70 microinches, and anodizing the outer region of said pore free aluminum coat to provide an electrically insulating and chemically protective barrier of aluminum oxide at least 1 microinch in thickness, said heat decomposable aluminum containing compound being applied in the form of a vapor, said vapor being mixed with an inert gas, the total vapor pressure being less than mm. Hg.

References Cited by the Examiner UNITED STATES PATENTS 2,700,212 1/1955 Flynn et al 20438.1 X 2,876,137 3/1959 Drummond 117l07.2 X 2,998,583 8/ 1961 Worcester 336-206 X FOREIGN PATENTS 427,599 8/1911 France.

OTHER REFERENCES Wiberg et a1, Uber Monomeren Aluminiumwasserstotf Al'H in Zeitschrift fur Anorganische und Allgemeine Chemie, vol. 272:221 and 226 (1953).

LEWIS H. MYERS, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

D. J. BADER, Assistant Examiner. 

